The present invention relates to titanium nitride (TiN) sputter targets, and more particularly, to TiN sputter targets formed by hot isostatic pressing; to a method for forming TiN films, and to TiN films formed by sputtering of the TiN targets.
The integration of a large number of components on a single integrated circuit chip requires sophisticated interconnections to minimize signal delays and simultaneously optimize the packing density. Aluminum has been widely used for contacts and interconnections in both bipolar and metal-oxide semiconductor (MOS) integrated circuits. However, the low-temperature interdiffusion of aluminum and silicon during contact sintering, passivation, or packaging of the device can result in gain degradation and increased junction leakage or even shorting of shallow junction devices. Device reliability can be improved by interposing a barrier layer between the Al and the Si which reduces the mass transport in the contact structure during processing or operation of the device.
TiN films have been proposed as diffusion barrier layers in very large scale integration (VLSI) metallization schemes and in solar cell top contacts. A TiN diffusion barrier layer prevents an undesired reaction between the contact metal such as aluminum and the substrate material such as silicon, and thus, permits the use of aluminum in cases where this would otherwise be prohibitive.
Reactive sputtering is a known method for forming TiN films. As those skilled in the art know, sputtering involves the transport of a material from a target to a substrate. Ejection of the target material is accomplished by bombarding the surface of the target with gas ions accelerated by high voltage. Particles of atomic dimensions are ejected from the target as a result of momentum transfer between incident ions and target material ions. These particles transverse the vacuum chamber and are subsequently deposited on the substrate in the form of a thin film.
To form a TiN film as part of a layered structure by reactive sputtering with N.sub.2 for microelectronics applications, the Al target cannot be present with the Ti target in the sputtering chamber. If both targets are located in the same chamber, AlN may form. Therefore, in reactive sputtering a TiN film typically is formed on a layer such as TiSi.sub.2 in a first sputtering chamber with a Ti target while an Al layer is formed on the TiN film in a second sputtering chamber with an Al target. As such, reactive sputtering is difficult to implement. According to Wittmer, "Barrier Layers: Principles and Applications in Microelectronics," J. Vac. Sci. Technol. A2(2), 273(1984), typical sensitivities for stoichiometric TiN thin films formed by reactive sputtering range between about 20 to 70 micron-ohm-cm. While these low resistivity levels are desirable they are difficult to achieve on an industrial scale.
Rapid thermal nitridization (RTN) is another method for forming TiN films. The method is advantageous because the TiN films are formed in situ. Typically, Ti is sputtered onto a substrate. The Ti film is then heated to about 1000.degree. C. and N.sub.2 is introduced so that a TiN film forms. The disadvantages of rapid thermal nitridization are that the TiN film thickness is difficult to control, the TiN film may be nonuniform, and hazardous gases such as NH.sub.3 are present.
Sputtering of a TiN target wherein the target is formed by a hot press method is another known method for forming a TiN film. The TiN target is formed by applying heat and pressure simultaneously to TiN powder at temperatures high enough for sintering of the TiN powder to occur. TiN targets formed by this method have a density of about 75% of the theoretical density of 100% pure TiN. Resistivities for TiN films formed by sputtering of hot pressed formed TiN targets tends to be about 100 micron-ohm-cm.
A sputtering target and method are desired wherein a layered structure having a TiN film therein can be formed in one sputter chamber and the resulting TiN film has a resistivity of less than about 70 micron-ohm-cm.